Spark ignition (SI) gasoline engines that use direct injection (DI), particularly those that are turbocharged, provide important efficiency increases over port fuel injection (PFI) engines and are rapidly increasing in use. The vaporization cooling from direct injection provides increased resistance to knock, thereby allowing operation at higher levels of turbocharging and/or compression ratio.
However, particulate emissions from DI gasoline engines are a health concern because they are small particles that can lodge in the lungs and are more than 10 times greater in mass per mile driven than emissions from PFI engines and are about 10-100 times greater in number per miles driven.
Gasoline particulate mass and number are presently regulated in Europe and more stringent regulations are expected. Regulations are expected in the US and California in the near future.
There is a need for a robust and low cost means to greatly reduce these particulate emissions with at least a near zero impact on vehicle fuel efficiency and preferably a zero or positive impact on vehicle fuel efficiency.